Dual cure coating compositions

ABSTRACT

The present invention relates to the use of (meth)acrylate functionalized amide acetals as reactive components with crosslinking agents and UV radiation to give new coatings compositions.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application60/615,359, filed Sep. 30, 2004.

FIELD OF THE INVENTION

The present invention relates to the use of methacrylate functionalizedamide acetals for dual cure (isocyanates/UV) coating compositions.

BACKGROUND OF THE INVENTION

Amide acetals have been used for example in copolymerization withpolyisocyanates as disclosed in U.S. Pat. No. 4,721,767. Cross-linkedamide acetal based coating compositions dry and cure rapidly without thepotential problems created by VOC emissions. Such coatings can be veryuseful, for example, in the automotive coatings industry.

Co-owned and co-pending US Patent Publication 2005-007461 describespolymeric compositions containing amide acetal groups, which arecrosslinked by hydrolyzing the amide acetal groups, and subsequentlyreacting the hydroxyl groups and/or the amine functions that are formedto crosslink the composition.

Co-owned and co-pending U.S. patent application Ser. No. 10/960,656describes a catalytic process for making amide acetals from nitrites anddiethanolamines.

Co-owned and co-pending U.S. Patent Application 60/615,362 describes thesythesis of these (meth)acrylate functionalized amide acetals, and ishereby incorporated by reference in its entirety.

Co-owned and co-pending U.S. Patent Application 60/615,363 describes theuse of (meth)acrylate functionalized amide acetals in single-curecoatings.

The crosslinking (curing) of polymers is an important commercialactivity, useful, for example, in elastomers, in coatings, and inthermoset materials such as are used for electronics. Controlling whenand under what conditions crosslinking takes place is usually criticalsince once a polymer is crosslinked it is usually not “workable,” thatis it may not be reshaped. In some applications, such as coatings andelectronic applications it may be desirable or even mandatory that nolower molecular weight compounds be volatilized during or after thecrosslinking of the polymers, so as not to contaminate sensitiveequipment such as electronics, and/or to pollute the environment, as inthe case of coatings.

Numerous ways have been found to avoid the production of volatilecompounds during curing. For example, the reaction of epoxy groups withother groups such as hydroxyl groups may accomplish this result, but itis sometimes difficult to control after the ingredients are mixed.Furthermore, higher temperatures may be required for this operation. Toavoid these types of problems, especially in coatings which often mustbe cured under conditions close to ambient conditions and which oftenmust be stable for long periods before curing, other solutions have beenfound, such as the use of spiroorthoesters, see for example World PatentApplication 9731073. However new and/or improved methods of crosslinkingpolymers are needed.

For coatings, basecoat-clearcoat systems have found wide acceptance inthe past decade as automotive finishes. Continuing effort has beendirected to such coating systems to improve the overall appearance, theclarity of the topcoat, and the resistance to deterioration. Furthereffort has been directed to the development of coating compositionshaving low volatile organic content (VOC). A continuing need exists forcoating formulations which provide outstanding performancecharacteristics after application.

In repairing damage, such as dents to auto bodies, the original coatingin and around the damaged area is typically sanded or ground out bymechanical means. Some times the original coating is stripped off from aportion or off the entire auto body to expose the bare metal underneath.After repairing the damage, the repaired surface is coated, preferablywith low VOC coating compositions, typically in portable or permanentlow cost painting enclosures, vented to atmosphere to remove the organicsolvents from the freshly applied paint coatings in an environmentallysafe manner. Typically, the drying and curing of the freshly appliedpaint takes place within these enclosures. Furthermore, the foregoingdrying and curing steps take place within the enclosure to also preventthe wet paint from collecting dirt or other contaminants in the air.

As these paint enclosures take up significant floor space of typicalsmall auto body paint repair shops, these shops prefer to dry and curethese paints as fast as possible. More expensive enclosures arefrequently provided with heat sources, such as conventional heat lampslocated inside the enclosure to cure the freshly applied paint ataccelerated rates. Therefore, to provide more cost effective utilizationof shop floor space and to minimize fire hazards resulting from wetcoatings from solvent based coating compositions, there exists acontinuing need for low VOC fast curing coating formulations which cureunder ambient conditions while still providing outstanding performancecharacteristics.

The curing of coatings by UV and EB is well known to those skilled inthe art. See Chemistry and Technology of UV and EB Formulation forCoatings, Inks and Paints, Volume IV, Formulation, by C. Lowe, et al.,John Wiley & Sons, New York, 1996.

The present invention allows for a dual-cure coating system, whereby thecoating can be crosslinked by reaction with a crosslinker, such asisocyanate, and subsequently cured additionally by exposure to UV orelectron beam (EB) energy.

SUMMARY OF THE INVENTION

The present invention relates to a composition, comprising:

a (meth)acrylate amide acetal of the formula

wherein R₄₂-R₄₉ independently represent a hydrogen, C₁-C₂₀ alkyl, C₁-C₂₀alkenyl, C₁-C₂₀ alkynyl, C₁-C₂₀ aryl, C₁-C₂₀ alkyl ester, or C₁-C₂₀aralkyl group, said alkyl, alkenyl, alkynyl, aryl, or aralkyl may eachhave one or more substituents selected from the groups consisting ofhalo, alkoxy, imino, and dialkylamino;

R₄₁ is (CR₅₀R₅₁)_(n) wherein R₅₀ and R₅₁ are hydrogen, C₁-C₂₀ alkyl,C₁-C₂₀ alkenyl, C₁-C₂₀ alkynyl, C₁-C₂₀ aryl, C₁-C₂₀ alkyl ester, orC₁-C₂₀ aralkyl group;

R₅₂ is hydrogen or methyl;

n is 1-10;

a crosslinking moiety; and

a UV catalyst.

The invention further relates to a process for forming a coatingcomposition comprising (meth)acrylate amide acetals, said processcomprising reacting a (meth)acrylate amide acetal with a crosslinkingmoiety to produce a crosslinked coating, and subsequently exposing saidcrosslinked coating to UV radiation.

The present invention further relates to coatings made by the disclosedprocess, having improved coating properties. The coatings may be part ofa basecoat-clearcoat system.

DETAILS OF THE INVENTION

Co-owned and co-pending U.S. Patent Application 60/615,362 describes thesythesis of (meth)acrylate-functionalized amide acetals, and is herebyincorporated by reference in its entirety. These hydroxy amide acetalsare then reacted with materials capable of crosslinking. Both thepre-crosslinked and crosslinked materials form coatings, with thecrosslinked ones generally used as such.

The formula for these (meth)acrylate amide acetals is

wherein R₄₂-R₄₉ independently represent a hydrogen, C₁-C₂₀ alkyl, C₁-C₂₀alkenyl, C₁-C₂₀ alkynyl, C₁-C₂₀ aryl, C₁-C₂₀ alkyl ester, or C₁-C₂₀aralkyl group, said alkyl, alkenyl, alkynyl, aryl, or aralkyl may eachhave one or more substituents selected from the groups consisting ofhalo, alkoxy, imino, and dialkylamino; and R₄₁ is (CR₅₀R₅₁)_(n), whereinR₅₀ and R₅, are hydrogen, C₁-C₂₀ alkyl, C₁-C₂₀ alkenyl, C₁-C₂₀ alkynyl,C₁-C₂₀ aryl, C₁-C₂₀ alkyl ester, or C₁-C₂₀ aralkyl group;

where n is 1-10, and where R₅₂ is either hydrogen or methyl. It is moretypical that R₄₂-R₄₉ each independently represent hydrogen and C₁-C₁₀alkyl groups.

Generally, these (meth)acrylate amide acetals are reacted withcrosslinking moieties such as isocyanates to form coatings, followed bysubsequent UV radiation. Other mechanisms of forming coatings aredisclosed in co-owned and co-pending U.S. Pat. Application No.60/615,363. The coatings are generally polymeric in nature.

By polymers herein are meant those entities with number averagemolecular weight from about 100 to about 100,000. Preferably, the numberaverage molecular weight of the polymers is from about 100 to about10000.

By oligomers herein is meant those polymers which have a number averagemolecular weight less than about 3000.

In the crosslinkable compositions herein, amide acetals groups arepresent in some form (see below), and the crosslinking reaction can beinitiated when water comes in contact with these groups to hydrolyzethem. By water is meant water in the pure form, moisture, moist air,moist gas or mixture of gases, or any other aqueous or non-aqueous mediain which water may be present in a homogeneous or a heterogeneousmixture. Such media may be in the liquid form or the gaseous form.

When the amide acetal is simply hydrolyzed, amino hydroxy ester isformed which then converts to the amide diol as illustrated below. Theamino hydroxy ester and the amide diol exist simultaneously as thereaction of conversion of the amino hydroxy ester to amide diol can becontrolled by time, temperature, pH, and the urethane forming catalystpresent in the reaction mixture. An advantage of the amide diol is thatit demonstrates minimal yellowing in the finished product, beforereacting with crosslinking agent. A rapid reaction with thecross-linking agent avoids the yellowing of the amine functionality inthe product. Both of these hydrolyzed products are cross-linking agentsbecause of the presence of their dual reactive side. In the case of theamino hydroxy ester the reactive sites are the secondary amine and thehydroxyl groups. In the case of the amide diol the reactive groups arethe hydroxyls or diol:

Note that in this reaction, no relatively volatile low molecular weightproducts are produced. Since these reactions may be acid catalyzed someof the ring opening of the amide acetal may lead to cationicpolymerization rather than simple ring opening. Herein preferably themajor molar portion of the amide acetal present may simply ring open anddo not polymerize, more preferably at least about 75 mole percent, andespecially preferably at least 90 molar percent may simply ring open anddo not polymerize. The polymerization occurs generally at hightemperatures. It is of course recognized that, although only one amideacetal group is shown (i.e., the case when m=1), this reaction wouldapply for m=2, 3 and 4 as well.

In the compositions, and in the materials used in the processes herein,the amide acetal groups may be included by a variety of methods. In oneinstance, the amide acetal may be included as a “monomeric” compound,which may hydrolyze, thus providing reactive hydroxyl groups.

Alternatively, the amide acetal groups may be part of a (possibly lowmolecular weight) polymer. For example a dihydroxy amide acetal (whichhas not yet been hydrolyzed) may be reacted with an excess of adiisocyanate such as bis(4-isocyanatophenyl)methane (MDI), toluenediisocyanate (TDI), hexamethylene diisocyanate (HMDI) or isophoronediisocyanate (IPDI) to form an isocyanate ended “prepolymer”, which uponexposure to water undergoes hydrolysis of the amide acetal forminghydroxyl groups, which react with the remaining isocyanate groups tocrosslink the polymer. Since amide acetal often hydrolyze faster thanisocyanate reacts with water, this is believed to be main mode of thecrosslinking reaction for this type of polymer. Other diols such asethylene glycol or 1,4-butanediol may also be copolymerized into the(pre)polymer formed. It is noted that in this type of isocyanatecontaining (pre)polymer, the amide acetal group is (at least beforehydrolysis) part of the main chain (not on a branch) of the polymerformed.

Alternately, the amide acetal may be functionalized, for example, viareaction of (mono)hydroxy amide acetal with isocyanate to give urethaneamide acetal, or with diisocyanates, for example, 1,6-hexamethylenediisocyanate, to give diurethane diamide acetals, or DESMODUR 3300 whichcontains multifunctional isocyanates, a triisocyanate, to give thecorresponding multifunctional urethane amide acetals. Many of thesecompounds are novel.

An example of the cross-linking agent, or second polymer with functionalgroups capable of reacting with hydroxyl or secondary amines, for(O═C═N

_(n>2)R₆₀the amide acetal is as follows:wherein R₆₀ is a hydrocarbyl structure.

Examples of suitable polyisocyanates include aromatic, aliphatic orcycloaliphatic di-, tri- or tetra-isocyanates, including polyisocyanateshaving isocyanurate structural units, such as, the isocyanurate ofhexamethylene diisocyanate and isocyanurate of isophorone diisocyanate;the adduct of 2 molecules of a diisocyanate, such as, hexamethylenediisocyanate and a diol such as, ethylene glycol; uretidiones ofhexamethylene diisocyanate; uretidiones of isophorone diisocyanate orisophorone diisocyanate; the adduct of trimethylol propane andmeta-tetramethylxylylene diisocyanate.

Additional examples of suitable polyisocyanates include 1,2-propylenediisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate,2,3-butylene diisocyanate, hexamethylene diisocyanate, octamethylenediisocyanate, 2,2,4-trimethyl hexamethylene diisocyanate,2,4,4-trimethyl hexamethylene diisocyanate, dodecamethylenediisocyanate, omega, omega -dipropyl ether diisocyanate,1,3-cyclopentane diisocyanate, 1,2-cyclohexane diisocyanate,1,4-cyclohexane diisocyanate, isophorone diisocyanate,4-methyl-1,3-diisocyanatocyclohexane, trans-vinylidene diisocyanate,dicyclohexylmethane-4,4′-diisocyanate,3,3′-dimethyl-dicyclohexylmethane4,4′-diisocyanate, a toluenediisocyanate, 1,3-bis(1-isocyanato1-methylethyl)benzene,1,4-bis(1-isocyanato-1-methylethyl)benzene,1,3-bis(isocyanatomethyl)benzene, xylene diisocyanate,1,5-dimethyl-2,4-bis(isocyanatomethyl)benzene,1,5-dimethyl-2,4-bis(2-isocyanatoethyl)benzene,1,3,5-triethyl-2,4-bis(isocyanatomethyl)benzene,4,4′-diisocyanatodiphenyl, 3,3′-dichloro-4,4′-diisocyanatodiphenyl,3,3′-diphenyl-4,4′-diisocyanatodiphenyl,3,3′-dimethoxy-4,4′-diisocyanatodiphenyl,4,4′-diisocyanatodiphenylmethane,3,3′-dimethyl-4,4′-diisocyanatodiphenyl methane, adiisocyanatonaphthalene, polyisocyanates having isocyanaurate structuralunits, the adduct of 2 molecules of a diisocyanate, such as,hexamethylene diisocyanate or isophorone diisocyanate, and a diol suchas ethylene glycol, the adduct of 3 molecules of hexamethylenediisocyanate and 1 molecule of water (available under the trademarkDesmodur® N from Bayer Corporation of Pittsburgh, Pa.), the adduct of 1molecule of trimethylol propane and 3 molecules of toluene diisocyanate(available under the trademark Desmodur® L from Bayer Corporation), theadduct of 1 molecule of trimethylol propane and 3 molecules ofisophorone diisocyanate, compounds such as 1,3,5-triisocyanato benzeneand 2,4,6-triisocyanatotoluene, and the adduct of 1 molecule ofpentaerythritol and 4 molecules of toluene diisocyanate.

In one instance a first polymer containing intact (before hydrolysis)amide acetal groups, and a crosslinking agent containing firstfunctional groups react with hydroxyl or secondary amine groups. Thecrosslinking agent may be a monomeric compound such as a diisocyanatesuch as MDI, TDI, HMDI or IPDI, or an epoxy resin, or may be a polymercontaining first functional groups. For example it may be (meth)acrylatecopolymer containing repeat units derived from 2-isocyanatoethyl(meth)acrylate or glycidyl (meth)acrylate. It is also possible that thefirst polymer and the crosslinking agent are “combined” in the samepolymer. For example one can copolymerize an amide acetal with2-isocyanatoethyl (meth)acrylate or glycidyl (meth)acrylate andoptionally other copolymerizable monomers. When that single polymer isexposed to moisture, presumably the amide acetal groups will hydrolyzeforming amino hydroxy groups (which eventually convert to hydroxylgroups as shown previously), which in turn will react with theisocyanate, carboxylic acid anhydride, melamine, silane(s) or epoxidegroups, whichever are present. These materials may be combined as asingle polymer or may be more than one substance.

In one preferred embodiment of this invention, a second polymer whichhas second functional groups capable of reacting with hydroxyl orsecondary amines has a number average molecular weight less than 3000. Apreferred functionality for this second polymer is isocyanate.

A specific example of the cross-linking agent, or second polymer withfunctional groups capable of reacting with hydroxyl or secondary amines,used here is the Desmodur® 3300 compound from Bayer. The idealizedstructure of Desmodur® 3300 is given as follows (also, pentamer,heptamer and higher molecular weight species can be present):

The amide acetal may also be present in the polymer as part of a branch.For example, a monohydroxylamide acetal may be converted to a(meth)acrylate ester by esterification and the resulting (meth)acrylicester,

where A is H for acrylates and CH₃ for meth(acrylates), may be freeradically copolymerized with other free radically copolymerizablemonomers such as meth(acrylates) and styrenes. Analogous variations willbe obvious to the skilled artisan.

Also present in these compositions, as amide acetals and the processesin which they are used, is a material having a first or secondfunctional group which reacts with hydroxyl or secondary amine groups.This reaction should take place under the conditions chosen for thecrosslinking reaction. These conditions may be ambient conditions orheating or other conditions that may be used to prod the reaction toproceed. Preferably the reaction with hydroxyl or secondary amine groupsshould not produce any volatile low molecular weight compounds, exceptthose normally found in air (CO₂, water, etc.) Typical groups whichreact with hydroxyl or secondary amine groups include isocyanates(including isocyanurate trimers), epoxides, carboxylic acid anhydrides(especially those which are parts of polymers), melamine, and silane(s).Isocyanates, melamine and silane are especially preferred for coatings.

In any of the compositions herein, the polymeric materials may rangefrom relatively low to relatively high molecular weight. It is preferredthat they be of relatively low molecular weight so as to keep theviscosity of the compositions before crosslinking low, so as to avoid orminimize the need for solvent(s).

The compositions herein may contain water. It is to be understood thatas the water contacts the amide acetal groups present in thecomposition, the amide acetal groups will start to hydrolyze, eventuallyleading to crosslinking of the composition. The water may be introducedin a variety of ways. For example, especially in the case of a coatingthe water may introduced into the uncrosslinked or crosslinking (whilethe crosslinking is taking place) coating by absorption from the air.This is very convenient for making an uncrosslinked coating compositionwhich is stable until exposed to (moist) air. Alternatively water may bemixed in a mixing head or spray mixing head (for a coating) just beforecrosslinking is to take place. This is particularly useful for makingthicker crosslinked items such as electronic encapsulants wherediffusion of moisture into a thicker section will take longer. Theintroduction of water can be at a point where the final shape of thepolymeric crosslinked part can be formed before crosslinking takesplace.

Other materials which may optionally be present in the compositions andprocesses include one or more solvents (and are meant to act only assolvents). These preferably do not contain groups such as hydroxyl orprimary or secondary amino which can react with either the first orsecond functional groups and/or amide acetals. One or more catalysts forthe hydrolysis of amide acetals may be present. These are typicallyBrönsted acids, but these acids should not be so strong as causesubstantial cationic ring opening polymerization of the amide acetalsand/or epoxides which may be present. If substantial cationic ringopening polymerization of amide acetal groups takes place, this canoften lead to premature crosslinking of the composition. The samecaveats may be said for any catalysts which may be present whichcatalyze the reaction of hydroxyl groups or the amino hydroxy groupswith the first or second functional groups. What these catalysts may bewill depend on what the first or second functional group(s) present are.Such catalysts are known in the art.

Some of the suitable catalysts for polyisocyanate can include one ormore tin compounds, tertiary amines or a combination thereof; and one ormore aforedescribed acid catalyst. Suitable tin compounds includedibutyl tin dilaurate, dibutyl tin diacetate, stannous octoate, anddibutyl tin oxide. Dibutyl tin dilaurate is preferred. Suitable tertiaryamines include triethylene diamine. One commercially available catalystthat can be used is Fastcat® 4202 dibutyl tin dilaurate sold byElf-AtoChem North America, Inc. Philadelphia, Pa. It is acknowledgedthat one skilled in the art could use acetic acid or such weak acids toblock the activity of the catalyst.

The present compositions, and the process for making them crosslinked,are useful as encapsulants, sealants, and coatings. The coatingcomposition of this invention can be used as a clear coat that isapplied over a pigmented base coat that may a pigmented version of thecomposition of this invention or another type of a pigmented base coat.The clear coating can be in solution or in dispersion form.

Typically, a clear coating is then applied over the base coating beforethe base coating is fully cured, a so called “wet-on-wet process”, andthe base coating and clear coating are then fully cured at ambienttemperatures or can be cured by heating to elevated temperatures of 40°C. to 100° C. for 15 to 45 minutes. The base coating and clear coatingpreferably have a dry coating thickness ranging from 25 to 75 micronsand 25 to 100 microns, respectively. By “crosslinker functionality” ismeant is the average number of functional groups per molecule. If thefunctionality of the crosslinker is too low, disruption of the basecoatflake orientation may occur. This disruption is measured by flop. Thehigher the value of flop the lower the amount of flake orientationdisruption. Less disruption of the flake orientation is seen with acrosslinker which has >3.1 average functionality and a viscosity at 100%solids at 23C. of >700 mPas, preferably >900 mPas, and mostpreferably >1000 mPas. These values are measured with a colormeasurement device and compared to a commercial standard.

The novel coating composition may be used as a base coat or as apigmented monocoat topcoat. Both of these compositions require thepresence of pigments. Typically, a pigment-to-binder ratio of 0.1/100 to200/100 is used depending on the color and type of pigment used. Thepigments are formulated into mill bases by conventional procedures, suchas, grinding, sand milling, and high speed mixing. Generally, the millbase comprises pigment and a dispersant in an aqueous medium. The millbase is added in an appropriate amount to the coating composition withmixing to form a pigmented coating composition.

Any of the conventionally-used organic and inorganic pigments, such as,white pigments, like, titanium dioxide, color pigments, metallic flakes,such as, aluminum flake, special effects pigments, such as, coated micaflakes, coated aluminum flakes and the like and extender pigments can beused. It may be desirable to add flow control additives.

The novel coating composition may be used as a primer in which casetypical pigments used in primers would be added, such as, carbon black,barytes, silica, iron oxide and other pigments that are commonly used inprimers in a pigment-to-binder ratio of 150/100 to 300/100.

The coating composition can be applied by conventional techniques, suchas, spraying, electrostatic spraying, dipping, brushing, and flowcoating.

The coating composition is particularly useful for the repair andrefinish of automobile bodies and truck bodies and parts as a clearcoat, pigmented base coat, or as a primer. The novel composition hasuses for coating any and all items manufactured and painted byautomobile sub-suppliers, frame rails, commercial trucks and truckbodies, including but not limited to beverage bodies, utility bodies,ready mix concrete delivery vehicle bodies, waste hauling vehiclebodies, and fire and emergency vehicle bodies, as well as any potentialattachments or components to such truck bodies, buses, farm andconstruction equipment, truck caps and covers, commercial trailers,consumer trailers, recreational vehicles, including but not limited to,motor homes, campers, conversion vans, vans, large commercial aircraftand small pleasure aircraft, pleasure vehicles, such as, snow mobiles,all terrain vehicles, personal watercraft, motorcycles, and boats. Thenovel composition also can be used as a coating for industrial andcommercial new construction and maintenance thereof; cement and woodfloors; walls of commercial and residential structures, such as, officebuildings and homes; amusement park equipment; concrete surfaces, suchas parking lots and drive ways; asphalt and concrete road surface, woodsubstrates, marine surfaces; outdoor structures, such as bridges,towers; coil coating; railroad cars; printed circuit boards; machinery;OEM tools; signs; fiberglass structures; sporting goods; and sportingequipment.

This makes these coatings particularly useful for repainting oftransportation vehicles in the field. An advantage of the presentmaterials and processes in encapsulants and sealants is that when amideacetals are used in crosslinking reactions the resulting product doesnot shrink, or shrink as much as usual in a typical crosslinkingreaction. This means any volume to be filled by the crosslinked materialwill be more reliably filled with a reduced possibility of voids beingpresent due to shrinkage during crosslinking.

For whatever uses they are put to, the compositions, and the materialsused in the processes described herein may contain other materials whichare conventionally used in such uses. For example, for use asencapsulants and sealants the composition may contain fillers, pigments,and/or antioxidants.

For coatings there may be a myriad of other ingredients present, some ofwhich are described below. In particular there may be other polymers(especially of low molecular weight, “functionalized oligomers”) whichare either inert or have functional group(s) other than those that mayact as the materials comprising amide acetals and also react with otherreactive materials in the coating composition.

Representative of the functionalized oligomers that can be employed ascomponents or potential cross-linking agents of the coatings are thefollowing:

Acid Oligomers: The reaction product of multifunctional alcohols such aspentaerythritol, hexanediol, trimethylol propane, and the like, withcyclic monomeric anhydrides such as hexahydrophthalic anhydride,methylhexahydrophthalic anhydride, and the like.

Hydroxyl Oligomers: The above acid oligomers further reacted withmonofunctional epoxies such as butylene oxide, propylene oxide, and thelike.

Anhydride Oligomers: The above acid oligomers further reacted withketene.

Silane Oligomers: The above hydroxyl oligomers further reacted withisocyanato propyltrimethoxy silane.

Epoxy Oligomers: The diglycidyl ester of cyclohexane dicarboxylic acid,such as Araldite® CY-184 from Ciba Geigy, and cycloaliphatic epoxies,such as ERL®-4221, and the like from Union Carbide.

Aldimine Oligomers: The reaction product of isobutyraldehyde withdiamines such as isophorone diamine, and the like.

Ketimine Oligomers: The reaction product of methyl isobutyl ketone withdiamines such as isophorone diamine.

Melamine Oligomers: Commercially available melamines such as CYMEL® 1168from Cytec Industries, and the like.

AB-Functionalized Oligomers: Acid/hydroxyl functional oligomers made byfurther reacting the above acid oligomers with 50%, based onequivalents, of monofunctional epoxy such as butylene oxide or blends ofthe hydroxyl and acid oligomers mentioned above or any other blenddepicted above.

CD-Functionalized Crosslinkers: Epoxy/hydroxyl functional crosslinkerssuch as the polyglycidyl ether of Sorbitol DCE-358® from Dixie Chemicalor blends of the hydroxyl oligomers and epoxy crosslinkers mentionedabove or any other blend as depicted above.

The compositions of this invention may additionally contain a binder ofa noncyclic oligomer, i.e., one that is linear or aromatic. Suchnoncyclic oligomers can include, for instance, succinic anhydride- orphthalic anhydride-derived moieties in the Acid Oligomers: such asdescribed above.

Preferred functionalized oligomers have weight average molecular weightnot exceeding about 3,000 with a polydispersity not exceeding about 1.5;more preferred oligomers have molecular weight not exceeding about 2,500and polydispersity not exceeding about 1.4; most preferred oligomershave molecular weight not exceeding about 2,200, and polydispersity notexceeding about 1.25. Typically, compositions will comprise from about20 to about 80 weight percent of the functionalized oligomer based onthe total weight of amide acetal-containing compound in the coating.Preferably compositions will comprise from about 30 to about 70 weightpercent of the functionalized oligomer based on the total weight of theamide acetal-containing compound in the coating. More preferablycompositions will comprise from about 40 to about 60 weight percent ofthe functionalized oligomer based on the total weight of amideacetal-containing compound in the coating. Other additives also includepolyaspartic esters, which are the reaction product of diamines, suchas, isopherone diamine with dialkyl maleates, such as, diethyl maleate.

The coating compositions may be formulated into high solids coatingsystems dissolved in at least one solvent. The solvent is usuallyorganic. Preferred solvents include aromatic hydrocarbons such aspetroleum naphtha or xylenes; ketones such as methyl amyl ketone, methylisobutyl ketone, methyl ethyl ketone or acetone; esters such as butylacetate or hexyl acetate; and glycol ether esters such as propyleneglycol monomethyl ether acetate.

The coating compositions can also contain a binder of an acrylic polymerof weight average molecular weight greater than 3,000, or a conventionalpolyester such as SCD®-1040 from Etna Product Inc. for improvedappearance, sag resistance, flow and leveling and such. The acrylicpolymer can be composed of typical monomers such as acrylates,methacrylates, styrene and the like and functional monomers such ashydroxy ethyl acrylate, glycidyl methacrylate, or gammamethacrylylpropyl trimethoxysilane and the like.

The coating compositions can also contain a binder of a dispersedacrylic component which is a polymer particle dispersed in an organicmedia, which particle is stabilized by what is known as stericstabilization. Hereafter, the dispersed phase or particle, sheathed by asteric barrier, will be referred to as the “macromolecular polymer” or“core”. The stabilizer forming the steric barrier, attached to thiscore, will be referred to as the “macromonomer chains” or “arms”.

The dispersed polymer contains about 10 to 90%, preferably 50 to 80%, byweight, based on the weight of the dispersed polymer, of a highmolecular weight core having a weight average molecular weight of about50,000 to 500,000. The preferred average particle size is 0.1 to 0.5microns. The arms, attached to the core, make up about 10 to 90%,preferably 10 to 59%, by weight of the dispersed polymer, and have aweight average molecular weight of about 1,000 to 30,000, preferably1,000 to 10,000. The macromolecular core of the dispersed polymer iscomprised of polymerized acrylic monomer(s) optionally copolymerizedwith ethylenically unsaturated monomer(s). Suitable monomers includestyrene, alkyl acrylate or methacrylate, ethylenically unsaturatedmonocarboxylic acid, and/or silane-containing monomers. Such monomers asmethyl methacrylate contribute to a high Tg (glass transitiontemperature) dispersed polymer, whereas such “softening” monomers asbutyl acrylate or 2-ethylhexylacrylate contribute to a low Tg dispersedpolymer. Other optional monomers are hydroxyalkyl acrylates ormethacrylates or acrylonitrile. Optionally, the macromolecular core canbe crosslinked through the use of diacrylates or dimethacrylates such asallyl methacrylate or post reaction of hydroxyl moieties withpolyfunctional isocyanates. The macromonomer arms attached to the corecan contain polymerized monomers of alkyl methacrylate, alkyl acrylate,each having 1 to 12 carbon atoms in the alkyl group, as well as glycidylacrylate or glycidyl methacrylate or ethylenically unsaturatedmonocarboxylic acid for anchoring and/or crosslinking. Typically usefulhydroxy-containing monomers are hydroxy alkyl acrylates or methacrylatesas described above.

The coating compositions can also contain conventional additives such aspigments, stabilizers, rheology control agents, flow agents, tougheningagents and fillers. Such additional additives will, of course, depend onthe intended use of the coating composition. Fillers, pigments, andother additives that would adversely effect the clarity of the curedcoating will not be included if the composition is intended as a clearcoating.

The coating compositions are typically applied to a substrate byconventional techniques such as spraying, electrostatic spraying, rollercoating, dipping or brushing. As mentioned above atmospheric moisturemay “diffuse” into the coating and cause curing, or alternatively justbefore the coating is applied it is mixed with an appropriate amount ofwater, as in a mixing spray head. Under these latter conditions it isimportant to apply the coating before it crosslinks. The presentformulations are particularly useful as a clear coating for outdoorarticles, such as automobile and other vehicle body parts. The substrateis generally prepared with a primer and or a color coat or other surfacepreparation prior to coating with the present compositions.

A layer of a coating composition is cured under ambient conditions inthe range of 30 minutes to 24 hours, preferably in the range of 30minutes to 3 hours to form a coating on the substrate having the desiredcoating properties. It is understood that the actual curing time dependsupon the thickness of the applied layer and on any additional mechanicalaids, such as, fans that assist in continuously flowing air over thecoated substrate to accelerate the cure rate. If desired, the cure ratemay be further accelerated by baking the coated substrate attemperatures generally in the range of from about 60° C. to 150° C. fora period of about 15 to 90 minutes. The foregoing baking step isparticularly useful under OEM (Original Equipment Manufacture)conditions.

In the present invention, the crosslinked coating is exposed to UVradiation at various wavelengths and fluxes. In order for the coating tobe cured by UV radiation, a photoinitiator is added to the coatingbefore cure and generally before crosslinking. There are manyphotoinitiators available for use in UV curing; any compound capable ofgenerating radicals upon UV exposure is acceptable. One pertinentreference is “A Compilation of Photoinitiators” by Kurt Dietliker, 2002SITA Technology Ltd., Edinburgh. Non-limiting examples of appropriatephotoinitiators include Phenyl bis(2,4,6trimethylbenzoyl-phosphineoxide), generally in solution form, with acetone being one usefulsolvent.

These and other features and advantages of the present invention will bemore readily understood, by those of ordinary skill in the art, from areading of the following detailed description. It is to be appreciatedthose certain features of the invention, which are, for clarity,described above and below in the context of separate embodiments, mayalso be provided in combination in a single embodiment. Conversely,various features of the invention that are, for brevity, described inthe context of a single embodiment, may also be provided separately orin any sub-combination. In addition, references in the singular may alsoinclude the plural (for example, “a” and “an” may refer to one, or oneor more) unless the context specifically states otherwise.

The use of numerical values in the various ranges specified in thisapplication, unless expressly indicated otherwise, are stated asapproximations as though the minimum and maximum values within thestated ranges were both preceded by the word “about.” In this mannerslight variations above and below the stated ranges can be used toachieve substantially the same results as values within the ranges.Also, the disclosure of these ranges is intended as a continuous rangeincluding every value between the minimum and maximum values.

Unless otherwise stated, all chemicals and reagents were used asreceived from Aldrich Chemical Co., Milwaukee, Wis.

EXAMPLES Example 1

The methacrylate amide acetal used in this series of experiments wasmade

in accordance with the procedures found in co-pending and co-owned U.S.Patent Application 60/615,362, hereby incorporated by reference in itsentirety.:The following compositions were prepared:Composition A (Control)

Wt (g) Amide Acetal Methacrylate 2.97 Di-isocyantohexane 1.68 DibutylTin Dilaurate (1.58 g in 3.42 g in propylene glycol 0.05 methyl etheracetate (PGMEA)) Dodecylbenzene Sulfonic Acid Solution (2.0 g in 3.0 gPGMEA) 0.05Procedure: The amide acetal methacrylate and the isocyanate were addedto a vial. To the resulting solution was added the dibutyl tindilauratesolution. After a few minutes an exothermic reaction occurred. After thereaction cooled down the acid solution was added. The resulting solutionwas poured on two glass plates and allowed to dry over night, resultingin a slight cloudy soft coating. See below for UV exposure data.Composition B:

Wt (g) Amide Acetal Methacrylate 2.97 Di-isocyantohexane 1.68 DibutylTin Dilaurate (1.58 g in 3.42 g of PGMEA) 0.05 Dodecylbenzene SulfonicAcid Solution (2.0 g in 3.0 g 0.05 PGMEA) Phenylbis(2,4,6-trimethylbenzoyl-Phosphine oxide) 1.00 mL solution (UVcatalyst; 6.59 g in 80 mL acetone) (via syringe)Procedure: The amide acetal methacrylate and the isocyanate were addedto a vial. To the resulting solution was added the dibutyl tin dilauratesolution. After a few minutes an exothermic reaction occurred. After thereaction cooled down the acid solution was added, followed by the UVcatalyst solution. The resulting solution was poured on two glass platesand allowed to dry over night, resulting in a slight cloudy softcoating. See below for UV exposure data.Composition C:

Wt (g) Amide Acetal Methacrylate 2.33 Di-isocyantohexane 1.00 Desmodur3300 0.32 Dibutyl Tin Dilaurate (1.58 g in 3.42 g of PGMEA) 0.05Dodecylbenzene Sulfonic Acid Solution (2.0 g in 3.0 g 0.05 PGMEA) Phenylbis(2,4,6-trimethylbenzoyl-Phosphine oxide) 0.90 mL solution (UVCatalyst; 6.59 g in 80 mL acetone) (via syringe)Procedure: The amide acetal methacrylate and the isocyanates(Di-isocyantohexane Desmodur 3300) were added to a vial. To theresulting solution was added the dibutyl tindilaurate solution. After afew minutes an exothermic reaction occurred. After the reaction cooleddown the acid solution was added, followed by the UV catalyst solution.The resulting solution was poured on two glass plates and allowed to dryover night, resulting in a clear tacky coating. See below for UVexposure data.

One of each of the plates were exposed to UV radiation as outlinedbelow:

Belt Speed 20 ft/min.

UV A: 1143 mJ/cm2 (energy) (3.6 watts/cm2 (flux))

UV B: 356 mJ/cm2 (1.08 watts/cm2)

UV C: 29 mJ/cm2 (0.092 watts/cm2)

The hardness of the unexposed coating to that of the UV exposed coatingwere test and tabulated in the following table

Composition Unexposed (newtons/mm2) UV Exposed (newtons/mm2) A (control)0.29 0.27 (scan twice) B 0.49 124 (scan twice) C 0.15 151 (one scan)

1. A composition, comprising: a (meth)acrylate amide acetal of theformula

 wherein R₄₂-R₄₉ independently represent a hydrogen, C₁-C₂₀ alkyl,C₁-C₂₀ alkenyl, C₁-C₂₀ alkynyl, C₁-C₂₀ aryl, C₁-C₂₀ alkyl ester, orC₁-C₂₀ aralkyl group, said alkyl, alkenyl, alkynyl, aryl, or aralkyl mayeach have one or more substituents selected from the groups consistingof halo, alkoxy, imino, and dialkylamino; R₄₁ is (CR₅₀R₅₁)_(n) whereinR₅₀ and R₅₁ are hydrogen, C₁-C₂₀ alkyl, C₁-C₂₀ alkenyl, C₁-C₂₀ alkynyl,C₁-C₂₀ aryl, C₁-C₂₀ alkyl ester, or C₁-C₂₀ aralkyl group; R₅₂ ishydrogen or methyl; n is 1-10; a crosslinking moiety; and a UV catalyst.2. The composition of claim 1, wherein the crosslinking moiety isselected from the group consisting of isocyanates, epoxides, carboxylicacid anhydrides, melamines, and silane(s); and the UV catalyst is anycompound capable of generating radicals upon UV exposure.
 3. A processfor forming a coating composition comprising (meth)acrylate amideacetals of claim 1, said process comprising reacting a (meth)acrylateamide acetal with a crosslinking moiety to produce a crosslinkedcoating, and subsequently exposing said crosslinked coating to UVradiation.
 4. A coating made by the process of claim 3, having theproperties of clarity and hardness.
 5. The coating of claim 4 used aspart of a basecoat-clearcoat system.